Method of conditioning x-ray generators



May 13, 1941. J ATLEE 2,242,101 METHOD OF CONDiTIONING X-RAY GENERATORSFiled Nov. 25, 1940 INVENT OR.

BY 26 fflggg ATTORNEYS Patented Ma 13, 19.41

METHOD OF' CONDITIONING X-RAY GENERATORS Zed J. Atlee, Elmhurst, Ill.,assignor to General Electric X-Ray Corporation, Chicago, Ill., acorporation of New York 1 a Application November 25, 1940, Serial No.366,978

14 Claims.

My invention relates in general to anti-friction devices, and has moreparticular'reference 'to bearings, especially bearings for-service undervacuum conditions. g

"The present application is a continuation in part of my co-pendingapplicatiOm'SeriaI No. 284,273, filed July 13, 1939.

An important object of the invention is to provide means for processinga bearing in order, in a sense, to lubricate the same without using alubricant having a vapor pressure such as to cause evaporation of thelubricating medium and migration thereof from the bearing under thetemperature conditions to which the bearin is subjected when inoperation.

Another important object resides in providing a new method of insuringthat a bearing, operating under low pressure or vacuum conditions, shallretain its anti-friction qualities without resort to lubrication aspresently applied in bearings, the invention having as a'furtherimportant object the provision of a method of processing anti-frictiondevices of the character mentioned with a medium which has a vaporpressure sufficiently low so that it will not evaporate from the bearingand thus destroy the'vacuum condition; a further object being toutilize, as a lubricating medium, a'material such as barium, calcium,strontium, magnesium, chromium, cop per, gold, silver, zinc, lead,aluminum, gallium, iron, nickel, cobalt, zirconium, rhodium ormanganese, having a vaporpressure of the order of 10- mm. of mercury atatmospheric pressure and not to exceed 10- mm. of mercury at hightemperatures of the order of 200 centigrade, whereby the lubricatingmedium may not migrate from a treated bearing operating under lowpressure and high temperature conditions.

Another important object resides in processing a bearing particularlyfor use in X-ray generators to support a rotating element of the gen-'erator for operation within a sealed evacuated enclosure in which theoperating temperature at the processed bearing may reach the order of200 centlgrade and up.

Another important object resides in the provision of means for applyingthe lubricating medium to the bearing after the same has been sealedwithin the evacuated enclosure.

Another important object resides in applying a lubricating medium of thecharacter mentioned qualities but which will not migrate from thetreated surfaces even under conditions of high temperature and lowpressure through the mechanical cohesion of the filmed material and itslow vapor pressure.

Another important object resides in applying the material as a film onthe surfaces to be treated by providing a supply of said material inposition adjacent such surfaces, then evaporating or flashing thematerial, by heating the same, to produce vapor, and directing the vaportoward and upon the surfaces to be treated; a further object being toarrange the supply of material in a capsule or casing, preferably in theform of a hollow filamentary wire having a weakened wall portion throughwhich the vaporized material may be expelled, the casing or capsulebeing mounted with its weakened wall facing toward the surfaces to betreated; a further object being to utilize an electrical current flowingin said filamentary wire capsule for the purpose of vaporizing thematerial. Another important object is to provide means for deliveringelectrical current for flashing the material to a supply of the materialsealed within an evacuated chamber;

A further object is to provide an X-ray generator including a bearingenclosed in the sealed evacuated envelope of the generator, and inutilizing the stem on which the bearing is mounted as a circuit formingpart for the delivery of current to a supply of vaporizable materialwithin the envelope.

These and numerous other important objects, advantages, and inherentfunctions of the invention will become apparent as the same is I morefully understood from the following description, which, taken inconnection'with the accompanying drawing, discloses a preferredembodiment of the invention.

Referring tothe drawing,

Figure 1 is a sectional view taken through an X-ray generator providedwith a rotating anode supported by a bearing structure of a type adaptedfor treatment in accordance with my present invention;

Figure 2 is an enlarged sectional view taken substantially along theline 2-2 in Figure 1, illustrating one mode of applying my presentinvention;

Figure 3 is a sectional view taken substantially along the line 3-3 inFigure 2; and

Figure 4 is an enlarged view taken substantially along the line 4-4 inFigure 3.

To illustrate my invention I have shown on thedrawings an X-raygenerator Ii comprising a rotating anode 13 supported within a sealedenvelope I! on bearings l5, although it will be apparent, as thedescription proceeds, that my invention is not necessarily limited toX-ray generators or even necessarily to bearings for operation underconditions of high temperature and have chosen to demonstrate myinvention as applied in X-ray generators, in' the operation unusable.

of which 'such excessive conditions of high heat v and low pressure areencountered.

The generator shown, of course, includes acathode C of any usual orpreferred character, and the anode is supported by the bearing IE on aspindle l9, which is shown mounted on and supported by the envelope, Hat one end thereof.

As shown, the envelope has an extension 2|, with-' in which the anode 13is snugly di posedfor rota tion, the envelope having a reentrantsleeve-like portion 23 forming an annular space 25 between the envelopeextension 2| and the reentrant portion 23.

The spindle is has an outwardly extending portion which is provided withmeans 29 forming anv annular shoulder carrying an annular flanged member3| sealed thereon. The member 3| has a peripheral edge forming aglass-to-metal seal 33 with the inner end of the reentrant envelopeportion 23. This seal, through the member 3|, supports the spindle onthe envelope with a spindle portion 35 extending within the envelope,the anodebearings l being mounted on said inwardly extending spindleportion". 7 s

, It should be understood that X-ray generators function to produceX-rays in response to the activation of the anode by electronic actionestab lished by the operation of the cathode l3. This electronic actioncompris'esthe impingement of electrons emitted by the cathode upon atarget 31 forming a part of the anode, and such electronic impingementresults in the generation of relatively large quantities of heat, whichis dissipated thence through the body of the anode i3, and also into theinterior of the casing I'I.' When in operation, the temperatureofjtheX-ray generator and particularly of the anode may be of the order of 500centigrade.

In conditioning an X-ray-generator for operation, the envelope I1 istreated to remove all gases ous and other impurities, the same beingaccomplished by evacuating the envelope as by means of a molecularexhaust pump while heating the elements of the generator to a hightemperature in order to drive out gases occluded in the envelope and allof the elements contained therein.

The envelope finally is sealed after all impurities have been thuseliminated.

During the operation of the X-ray generator as such, the anode I3 isdesirably rotated at high speed, in order to minimize the danger ofoverheating and burning the target itself, as a result of electronimpact. Considerable dimculty has been encountered in providing meansfor supporting the anode for rotation during the life of the generator,under the excessively high temperature conditions and the low pressurenecessarily maintained within the envelope ILslnce it is not feasible toapply usual bearing lubrication because lubricants of the characterheretofore known will not remain in the bearings under the low pressurecondition necessarily maintained in the envelope, but will instantlyevaporate and become dissipated within the envelope, thus not onlyrobbing the bearings of lubricant but also destroying the vacuum in thetube and rendering the same inoperative. Consequently, it has notheretofore been considered feasible to lubricate bearings underconditions necessarily maintained in X-ray generators. Excessive bearingwear results, pare ticularly atthe high temperatures encountered in thegenerator, with the resultant development or anode vibration, whichrapidly renders the device Excessive bearing wear also results in theproduction of minute wear products, which also impair the operation'ofthe generator as the same becomedissipated from the bearings within theenvelope.

My present invention relates to a method of lubricating bearings in amanner avoiding the aforesaid difficulties, particularly encountered inX-ray generators having rotating anodes; but the invention is by nomeans limited to such particular' apparatus and, in fact, may be appliedto advantage in any bearing structure.

In practicing my invention, 1 select a suitable material adapted to beapplied asa vapor and to condense and form a film upon the bearingsurfaces to be treated, thesselected material desirably having severalqualities, including not only softness and flowability, with lowinternal coefficient of friction when in film-like form, but alsosufficient mechanical vcohesionto cause the filmed material to beretained upon the treated bearing surfaces, the property of "wetting"the bearing surfaces to be treated, low vapor pressure to preventevaporation at the pressures and temperatures to'which the treatedbearing is to be exposed, and, unless the bearing is' to be in operationin an oxygen-free atmosphere, the

lubricating material should not normally oxidize.

Where the bearing is applied in an evacuated)!- rayg generator, theproblem of oxidation of the filmed lubricating medium will not, ofcourse, be

encountered. However, if the treated bearing is for use in the ordinaryatmosphere, or elsewhere exposed. to oxidation, the lubricating mediumshould be of a character normally resisting oxidation. I

I have found that barium, calcium; strontium, magnesium, chromium,copper, gold, silver, aluminum, gallium, iron, cobalt, zirconium,rhodium, manganese and nickel are all of a nature adapted for use aslubricating media, in accordance with the teachings of my presentinvention; that combinations .of these materials may be used; and, infact, in treating bearings for use in x-ray generators, I prefer toemploy barium, as a lubricating film applied upon the bearing surfaces.The foregoing materials have vapor pressures of the order of 10- at'temperatures of the order of 200 centigrade and are therefore welladapted for use as lubricants in bearings operating under low pressureconditions. Where op-, erating pressures are relatively higher,- othermetals such as caesium, rubidium, sodium, lithium and potassium areavailable in addition to those specified for excessively low pressureservice.

Chromium, which normally will not oxidize,

' may be used in the treatment of bearings for operation in atmosphereor under other oxidimng conditions. i

The selected material is applied-upon the bearing surfaces, inaccordance with my present invention, by vaporizing the same anddirecting a stream of the vaporized material upon the bearing surfacesto be treated whereby thus to conthe vapor and form a thin film of thematerial upon the surfaces to betreated- Vaporization -anddeliveryof thematerlalupon the sur-- capsule. in any convenient manner, as by thepassageof an electrical current in orderto vaporize the materialwithinthe capsule and blowing the resultingvapor through the capsule openingand upon the surfaces to be processed. Alternately, the materialzmay beformed as a, filamentary wire, in which the desired lubricating elementisincorporated, and then passing an electrical current-through the wirein order to expel the. lubrieating medium as a vapor upon the surfacesto be treated. Such ires as thcriated tungsten and alloys of silver andthis manner. Heating coils of tungsten wire in pocketshape, with a smallquantity of the lubrieating-medium enclosed in thepocket, may sirnilarlybe used. As the tungsten wire is heated to the melting p int of themetal so enclosed, an. alloyof thelubricating medium .with the tung'stenwireI'may be formed onfthe surfaces of the. wire, and this alloy inturn may then be re-evaporated in order to produce afllm of thelubricating/ medium l pon the surface to ,be treated. This method issuitable for applying such mate isisss chromium, difiicul-tly obtainablein m tallic state and possessing high melting point. I

,Iprefer, however, in treating bearings for use inx-ray generators, toemploy a hollow filamentary wire W, preferably of iron ornickel,containing within the wire a quantityof the lubri-- eating material L,such as pure barium, the hollow wire being weakened by reducing its wallthickness along one side of the wire, as indicated.

'at'SWBy'p'ass-ing anelect'rical current through the wire W, thematerial L may be porized therein, the vapor products being brown outthrough'the weakened wall section S, and of course by supporting thewire with the surface S facing toward the bearing surfaces to'betreated, the vaporized medium, may be directed directly upon suchbearing surfaces.

shown in the drawings, theanode 13 comprises a'cylindrical body havingan open'end extending in the annular envelope, space 25 in positiontoencircle the seal 33 at the innerend of the'reentrant envelope portion23. The anode thus forms a shield for protecting the seal 33 fromdeterioration through impingement of stray electrons thereon. Theopposite end of the 'an-. ode'body is enclosed, as at 39, and ailords amounting for the target 31. Externally the'cylindrical walls of theanode form a seat on which is'se'curedthe rotor 4| of an electric motor,the

stator '43 of which encircles the envelope exten-' sijon 2 ,incooperative relationship with the rotor 4| wherebyto drivethe anodewithin the envlope when the stator 43 isv excited from any suitablesource of electrical power externally of the envelope. I

The spindle 35 extends within the cylindrical anode and carries thebearing means 15, said hearing means comprising in the illustratedembodinient a pair of roller bearings 44 and 46, in

spaced-apart position on thespindle portion 35.

zinc may be utilized in conventionally retained between the inner andouter race portions.

The anode l3 may, of course, be mounted on the bearing elements in anysuitable or preferred fashion, although I have shown the same in thedrawing clampingly secured on a cylindrical slecve-like anode mountingelement 85, upon which the cylindrical anode member I3 is fastened, thebearings being enclosed within the 1101-- ora plurality of globule 61applied within low bore 81 of the member 85.

The spindle portion 35 is formed with a shoulder- 41 providing aseatfforthe inner raceof the seat and held in position on the stempreferably by means of .a nut 5| threaded on the stem. The stem 35 isalso threaded to receive clamping nuts 53 and 55 between which isclampingly secured on the stem the inner race of the bearing 46, and aheat shield 51 may be provided for the bearing 46 and supported on theclamping nut 55 in position extending between the target-carrying end ofthe anode, in which maximum heat is encountered during the operation ofthe device. This shield serves .to protect the bearing from heatradiated from said;target-carrying portions of the anode,'and tends toequalize the temperature under which the bearings i l and 46 function.

The spindle I9 is provided with a longitudinally bearing 44,- thebearing being clamped in said extending duct 59 extending from theoutwardly exposed end of the spindle to a point in the spindle portion35 intermediate the bearings 44 and 46,- said duct'59 opening laterallyon the portion 35 within the bore or channel 81 of the anode supportelement 85. The outer end of the duct 51 is enlarged, and has sealedtherein .a. sleeve 6|, preferably. comprising forty-two percent nickelsteel, a material adapted to sealreadily with glass. A- leadconductor-63 is arranged in the duct 58 with one end of said conductorextending outwardlyof thesleeve' GI, and the other end pro? jectingthrough the end of the duct which opens on the spindle portion 35.Suitable insulating means 65, such as a. sleeve of magnesium silicate,

glass beads embracing the conductor within the duct 59, is provided forinsulating the conductor electrically from the stem IS in which it isarranged, the outer end of the duct being sealed preferably by means ofa glass the sleeve 6| around the conductor 63.

Within the space 81 I mount suitable support means for a supply of thelubricating material L, and utilize the conductor 63 and the spindle l9as circuitiforming means for electrically energiz- 55 ing the material Lto vaporize the same within the channel 81, in order toprocess thebearings 15. In. the illustrated embodiment this is accomplished' byarranging a length of the filamentary tubulan wire W on the stem portion35, saidwire being arranged to form loops 69 in position opposite thebearings l5, with the weakened surfaces of the wire portions formingsaid loops- 69 facing toward the bearings. The loops 69 are electricallyinterconnected, preferably in Each bearing comprises an outer racesecured on integral portionof series, in any. suitable fashion by meansof an the wire W extending between the loops 69. One of the loops iselectrically connected as by soldering or welding the same upon thespindle portion 35, the other loop being electrically connected with theend of the conductor 53 which is nel 81.. If desired, the spindle 35'may be provided with insulating means for supporting the wire, Wrigidly. inposition, although ordinarily additional support is notrequired since the wire exposed within the chanitself has sufficientrigidity to maintain itself in assembled position, at least until afterthe ma-- terial L has been flashed in processing the bearing l .I.,

It will be seen from the foregoing that'by con-" necting a suitablesource'of electrical potential between the outwardly exposed end ofthe'coriductor 63 and the spindle l9, an electrical heat ing current maybe caused to flow through the wire W in order to raise the temperatureof the wire toa point at which the material Lv'apo rizes, in order thus,sis-heretofore described," to cause the expulsion of vapor through theweakened wall S 'at the=loops 69 and thence upon the bearings.

The bearings preferably are thus processed for the application of a filmof the lubricating medium L thereon, after assembly in the envelopepinging upon the facing surfaces of the bearings,

which preferably are rotated-during the'fiashing of the material L,immediately condense upon the surfaces to form a film thereon, the innerface of the ,film wetting the surface material ofthe bearing and formingan alloy therewith which holds the-film in place; The rotation of" thebearings causes substantially all of 'the -sur faces thereof required'tobe treated to receive the coated film of the lubricating material; and

since the flash products are confined substan-' tially within thechamber 81, no migration of such products outwardly of the bearings andthe hollow anode is detectable, and the vacuum-condition within theenvelope is not in any way impaired as a result of the flashingoperation. I

In order to seal and protect the exposed end of the conductor 63, theouter end of the stem l9 may be threaded, as shown at l I, to receive acover cap 13, the outer end of which may be threaded as shown, orotherwise finished as de-' sired, said cap being preferably threadedforthe reception of heat dissipating means thereon by means of whichheat developed at the anode may, in part, be dissipated from thegenerator by conduction through the anode support sleeve 85, thebearings l5, and the spindle outwardly of the envelope l'l,

The flashing of the material L from the wire W may be controlled so thatthe-lubricating medium L may be repeatedly flashed on the bearingsurfaces, This may beaccomplished in any suitable manner, for example,by controlling the amount of heating current and the time of flowthrough the wire W. In thi manner, the lubrication of the bearings canbe renewed from time to time in a very simple manner.

It has been found that the best results are obtained where there isapparentlythe formationintegral part of the working-surface of thehearing. It will be understood that the working surface of the bearingmay be such that the first vaporized thin metallic coating applied willalloy therewith'and the second vaporized. thin metallic coating willalloy with the first, The life'of the lubrication is'not as long ifneither of the metal lic coatings has an-alloying action with the metalor'metals from which the working surf'ace ofth'ebe'a'ringis made. 1

- Excellent results have been obtained when the working surface ofthe'bearing has been formed to this't'y'pe of bearing are the following:Barium, zinc, rhagn'esium, strontium, aluminum, gold, copper, iron,nickel; cobalt, platinum, and chromium. While some of these ma terialsyielded results similar to those obtained barium, none gave any betterresults". It will be recognized that there is a possibility of twoormore different alloys being formed where the bearing surface is formedfrom an alloy: For

example, inemploying a bearing material of the type just mentioned,it'is possible that thellubri' eating-alloy formed may be abarium-cobalt layer, and since chromium is also present, ther'emay alsobeabarium-chromium layer.

i The lubricating-action has also been obtained by vaporizing bariumonto 18% chromium, 8%, nickel stainless steel bearing surfaces. In oneseries of tests, a layer of cobalt vaporized oh S. 'A. E. 52'--100'steel provided relatively slight lubrication and'vaporizedbarium alone provided very slight; lubrication, but just as soon as ,a

barium layer was'added on top of the cobalt, ex-j cellent lubricationdeveloped. This provesvery clearly thatat least one lubricating film isa com-1 bination of "cobalt and barium. 'I n'another test, a layer ofchromium vaporized on S. A. E. 52 -'10 0' steel showed relativelyslight'lubrication, but as barium was vaporized on top of the chromium,excellent lubrication was obtained even' superior to that obtained withcobalt.

.A combination layer of aluminum and. barium onS. A. E. 52-100 steelballs gave excellent lubrication. In addition, combination layers ofmanganese and'barium, rhodium and barium,fand zirconium and barium havebeen tried with somewhat similar success.

Generally speaking, it has been observed that the best results areobtained with certain'elements having similar chemical characteristicswhen alloyed with thin vaporized films of certainother elements of thealkali and alkaline earth metal groups. Among the elements havingsimilar chemicalcharacteristics which may be mentioned are cobalt,chromium, aluminum, zirconium, rhodium, manganese, iron and nickel.Among the elements which are preferably alloyed withthese elements byvaporization are barium,

. strontium, calcium, and magnesium. For exarr'rple, barium may bealloyed with any one of the elements mentioned, or with combinationsthereof, and the same is true of strontium, calcium, and magnesium. Analloy of chromium andalumi num alonejir'i air also appears to have somelubrieating properties when formed as a thin film .on the'workingsurface of a bearing, as herein described. 1 K

' Generally stated, the preferred lubricating" alloy combinations ofelements for the purpose of this inventionare combinations of'one ormore calcium, silvr,'-'-

of the metals of group 11a of the Mendelyeev Periodic System with one ormore metals of groups IVa, Va, VIa, VIIa, VIII, Ib, IIb, and/or IIIb,and one ormore elements of group VIa with one or more elements of group1111).

I have found that bearings treated in accordance with the teachings ofmy present invention are able to operate substantially without wear andwithout conventional lubrication throughout extended service periods,under excessive low pressure and high heat conditions. When used inX-ray generators, bearings processed in accordance with my presentinvention have an extended service life, usually outlasting the normallife of the generator itself.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction, andarrangement of the several parts without departing from the spirit andscope of the invention, nor sacrificing its attendant advantages, theforms herein disclosed being merely for the purpose of demonstrating theinvention.

The invention is hereby claimed as follows:

1. A method of conditioning an X-ray generator having an X-raygenerating element turnably supported by a bearing in an evacuatedcasing, which comprises vaporizing a lubricating metal in said casingand directing the metal so vaporized upon a working surface of thebearing to form a thin metallic lubricating film thereon.

2. A method of conditioning an X-ray generator having an X-raygenerating element turnably supported by a bearing in an evacuatedcasing, which comprises vaporizing a lubricating metal in said casing,directing the vaporized metal upon at least a portion of a workingsurface of the bearing to form a thin metallic lubricating film thereonand repeating said vaporization of said metal at intervals in order torenew said lubrication.

3. A method of conditioning an X-ray generator having an X-raygenerating element turnably supported by a bearing in an evacuatedcasing, which consists in applying a lubricating metal thereto invaporized condition and causing the metal to condense upon surfaces ofthe bearing.

4. A method of conditioning an X-ray generator having an X-raygenerating element tumably supported by a bearing in an evacuatedcasing, which consists in rotating said bearing while applying to thebearing surface a vaporized lubricating metal and causing said vaporizedmetal to condense on said bearing surface.

5. A method of conditioning an X-ray gen erator having an X-raygenerating element turnably supported by a bearing in an evacuatedcasing, which consists in rotating said bearing while applying to a partof the bearing surface a vaporized lubricating metal and causing saidvaporized metal to condense on said bearing surface.

6. A method of conditioning an X-ray generator having an X-raygenerating element turnably supported by a bearing in an evacuated cas--ing, which comprises vaporizing a lubricating metal in said casing,directing the metal so vaporized upon the working surface of the bearingto form a thin metallic lubricating film thereon, said metal being areadily oxidized metal having a vapor pressure not greater than 10- mm.of mercury at a temperature around 200 C.

"I. A method of conditioning an X-ray generator having an X-raygenerating element turnably supported by a bearing in an evacuatedcasing, which comprises vaporizing a lubricating metal in said casingand directing the metal so vaporized upon a working surface of thebearing to form a thin metallic lubricating film thereon, said metalbeing selected from the metals of group 1111 of the periodic system.

8. A method of conditioning an X-ray generator having an X-raygenerating element turnably supported by a bearing in an evacuatedcasing, which comprises vaporizing a lubricating metal in said casingand directing the metal so vaporized upon a working surface of thebearing to form a thin metallic lubricating film thereon, said metalbeing selected from the metals of group III!) of the periodic system.

9, A method of preparing and conditioning an X-ray generator having anX-ray generating element turnably supported in bearing means in anevacuated casing, which comprises vaporizing a metal in said casing inthe vicinity of said bearing means and condensing the metal so vaporizedupon a working surface of the bearing to form a thin metalliclubricating film thereon said metal being capable of wetting and formingan alloy with the working surface of said bearing.

1Q. A method of preparing and conditioning an X-ray generator having anX-ray generating element turnably supported in bearing means in anevacuated casing, which comprises forming the working surface of thebearing of a metal containing a metallic element selected from groupVIII of the periodic system; vaporizing another metal capable ofalloying with said element in the vicinity of said bearing surface andcondensing the metal so vaporized upon the working surface of saidbearing to form a thin metallic alloy lubricating film thereon.

11. A method of preparing and conditioning an X-ray generator having anX-ray generating element turnably supported in bearing means in anevacuated casing, which comprises forming the working surface of thebearing of a metal containing a metal selected from groups VIa, VIIa,VIII, Ib, IIb and III!) of the periodic system, vaporizing a metalselected from group 11a of the periodic system in the vicinity of saidworking surface and condensing the metal so vaporized upon said workingsurface to form a thin metallic lubricating film thereon.

12. A method as claimed in claim 11 in which the bearing contains cobaltand the vaporized metal comprises barium.

13. A method as claimed in claim 11 in which the bearing containschromium and the vaporized metal comprises barium.

14. A method as claimed in claim 11 in which the bearing containsaluminum and the vaporized'metal comprises barium.

ZED J. A'I'LEE.

